for the 21 the best mower we have used is the honda hrc216 hydro.we have really liked the hustler 37 walk behind that we have used for two seasons now. as for the bigger machines , our first rider was a mtd pro mz54.mechanicaly it has been excellent .we used a hustler z60 for 1 week,a lazer z for 2 weeks and did a demo of a grasshopper 60 z. best macine we ever used is our current kubota zd60.has 2 years use so far .we wont buy another rider without a diesl engine.